MEPS 357:51-66 (2008)  -  DOI: https://doi.org/10.3354/meps07331

ABSTRACT: Physical characteristics of pockmarks in Passamaquoddy Bay, Bay of Fundy, Canada were measured, including depth, benthic area, sidewall slope, orientation at longest diameter and an out-of-roundness estimate. Sedimentary holes of uncertain origin, ranging from 2.69 to 36.02 cm² in area, were discovered. Mean densities of 4.78 holes m^–2 inside and 3.88 holes m^–2 outside pockmarks were found. Geochemical measurements of cores of ~100 cm depth suggested that sedimentary microbial metabolism was different inside than outside pockmarks. The megabiota consisted of the sea star Asterias rubens, commonest outside pockmarks; the sea cucumber Cucumaria frondosa, commonest on pockmark bottoms; an unidentified bryozoan/hydrozoan and the filamentous bacterium Beggiatoa sp., commonest on pockmark sidewalls. During this study, 2 habitat types (A and B) were characterized by differences in (1) multibeam acoustic data, and (2) community structure. Two different patterns of benthic macro-infaunal community structure were related to upper and lower areas within Habitat A. Compared to reference sites, upper Habitat A pockmarks had significantly fewer species and lower densities. Consequently, pockmark community structure was also different, notably with absence or lower densities of taxa appearing late in the succession. Lower Habitat A pockmarks had smaller and more subtle differences in macro-infaunal community structure than reference locations outside pockmarks and the equilibrium species number varied with benthic area of each pockmark. Circumstantial evidence, including nMDS and species–area plots, dominance patterns, accumulated species number and density of benthic macrofaunal communities, supports the hypothesis that upper Habitat A pockmarks are at various stages in a pre-equilibrium succession. By contrast, all lower Habitat A pockmarks had already reached equilibrium levels.

KEY WORDS: Pockmarks · Macro-infaunal communities · Megabiota · Sedimentary holes